This invention generally relates to sedimentation apparatus for separating liquid from a mixture of liquid and solids, such as clarifiers or thickeners, and more particularly, this invention concerns a rotary clarifier or thickener having an improved device for skimming suspended solids or froth, hereinafter called scum, from the surface of the liquid therein.
Clarifiers and thickeners have been employed for many years in water pollution control plants and industrial waste treatment installations to remove solids from liquids. A current example of a rotary clarifier is disclosed in trade literature of the assignee of the present invention entitled, "Eimco Clari-Thickener.TM. Sludge Thickening Clarifier". As disclosed therein, scum is mechanically skimmed from the surface of the liquid in the clarifier, so that relatively clean effluent will overflow into an annular launder at the periphery of the clarifier tank. The skimmer includes a fixed portion and a pivotable portion connected to the outer end of the fixed portion. The pivotal portion is adapted to urge the scum into a scum box that is mounted to the clarifier tank. It is noted that the scum is induced to move toward the periphery of the clarifier by the outward flow of the effluent into the peripheral launder.
The U.S. Pat. No. 2,647,870 issued in August, 1953 to Kelly et al also describes a clarifier including a conventional skimmer mechanism for the removal of froth and scum similar to that used in the just mentioned prior art rotary clarifier.
U.S. Pat. No. 2,633,989 issued in April, 1953 to Kelly et al, discloses a variable level skimmer from liquid passing through an elongated tank (referred to therein as a skimming pond). The skimmer includes a level controller that employs a motor adapted to raise or lower a travelling framework to which the skimmer blades are attached.